1914] CROCKER fir DAVIS— DELAYED GERMINATION 291 



may easily weaken the coat, so that the imbibing embryo can rup- 

 ture it, for we shall see later that the evidence is strong that the 

 delay is due to the swelling force of the embryo being unable to break 

 the restraining coat. We must bear in mind also that without 



chemical decomposition 



the 



cellulose substances of the seed coats, but undoubtedly chemical 

 transformations as well as physical are brought about in the acid 

 and base-sensitive substances of the seed coat. 



Heating the seeds to 99-100 C. for 0.5 hr. in 2 per cent HO, 

 followed by o. 5 hr. in 2 per cent NaOH, the usual method of dis- 

 solving out the middle lamella of cell walls, dissolves away most 

 of the coat at the large end of the embryo and causes the embryo 

 to break the coat and elongate 200-400 per cent. All regions of 

 the coat were modified; in some cases the walls were apparently 

 largely dissolved away, leaving a thin lamella, and in others gelati- 

 nized and greatly swollen. Some color dissolved out of the wall in 

 the acid, but immediately upon transfer to the base the latter took 

 on a deep red color. Heating to 99-100 in 2 per cent NaOH 

 for o. 5 hr. gave similar results, and 0.5 per cent NaOH was almost 

 as effective. Even at room temperatures, similar but less marked 

 changes appeared in 2 per cent NaOH, and at this temperature 

 0.5 per cent caused noticeable exosmose of coat pigments and 

 decomposition of the coats within a half-hour. 



It is found that seeds treated with o. 3 N HC1 for 1 hr. at 40 C. 

 give 30-50 per cent germination in distilled water; much poorer 

 germination in 0.000001 mol. CuS0 4 , and none at all in 0.001 

 mol. CuS0 4 . As has been pointed out, the embryos with coats 

 partly removed germinate better in 0.000001 mol. CuS0 4 than in 

 distilled water. It seems that the copper is rather readily absorbed 

 by the gel-like coat and the consistency of the latter changed. 

 The absorption is evidenced by the coat turning a dark dull brown 

 rather rapidly in the stronger solution and slowly in the weaker. 

 The rather plastic gel of the coat becomes hard and brittle and is 

 easily cracked under the pressure of a scalpel. The hardening 

 takes place to a more marked degree in untreated seeds soaked in 

 water. Apparently this hardening of the coat gel increases the 



